Potential Degradation of Hexabromocyclododecane (HBCDD) in Sediments: Stereoisomer Specific Reaction of HBCDD with Reduced Sulfur Species or Fe(II) Bound to Iron Oxides

The individual degradation rates of the three dominant stereoisomers (alpha, beta, gamma) of hexabromocyclododecane (HBCDD) with bisulfide and polysulfides were investigated at pH 9-10 in methanol/water solutions at two different temperatures (25 °C and 40 °C). alpha-HBCDD reacts significantly slower than beta-HBCDD and gamma-HBCDD. It was also observed that the reaction of HBCDD with polysulfides is faster than with bisulfide. For the reaction of HBCDD with bisulfide, the experiments were performed in 20% water/80% methanol, 50% water/50% methanol and 80% water/20% methanol at 40 °C. It was determined that the solvent polarity affects the reaction and the second-order rate constants of beta-HBCDD and gamma-HBCDD with bisulfide are larger with higher percentage of water. Only one isomer of tetrabromocyclododecene (TBCDe-5) was identified as a degradation product of the reaction of HBCDD with reduced sulfur species. TBCDe-5 itself reacts about ten times slower with bisulfide and twenty times slower with polysulfide than HBCDD. The reaction of HBCDD isomers with Fe(II) bound to magnetite and goethite were performed in a pH range from 6.15 to 7.50 at room temperature. It was observed that Fe(II) bound to iron oxides is a more efficient reductant than aqueous solution of Fe(II) only to reduce HBCDD in sediments. The reaction of HBCDD with Fe(II) bound to iron oxides is also stereoisomer specific with alpha-HBCDD reacting much slower than beta-HBCDD and gamma-HBCDD. The reaction is pH dependent and it is faster with increased pH. The initial concentration of Fe(II) and HBCDD can affect the reaction rate. The reaction is negligible when all the Fe(II) is sorbed to magnetite and no Fe(II) remains dissolved. It was also observed that the reaction of 100 nM HBCDD is slower than the reaction of 1 µM HBCDD with Fe(II) bound to magnetite. In addition, natural organic matter (NOM) was found to inhibit the degradation of HBCDD by Fe(II) bound to iron oxides. The much slower abiotic reaction of alpha-HBCDD compared to beta-HBCDD and gamma-HBCDD could potentially contribute to the fact that alpha-HBCDD is found in higher concentrations in biological samples than gamma-HBCDD. The study demonstrates that bisulfides, polysulfides and Fe(II) bound to iron oxides can play a significant role in the degradation of HBCDD in sediments

Nitrogen-Doped Porous Carbon Derived from Bamboo Shoot as Solid Base Catalyst for Knoevenagel Condensation and Transesterification Reactions

Highly porous nitrogen-doped carbons derived from bamboo shoots (BSNCs) were prepared through an in-situ synthesis method. The results showed that BSNCs had a large specific surface area, a relatively high nitrogen content and hierarchically porous structures. The catalytic properties of BSNCs were evaluated based on Knoevenagel condensation and transesterification reactions. Deprotonated BSNC-700 exhibited high efficiency for the model reactions as a solid base catalyst, and the superior sample deprotonated in tBuOK solution with a concentration of 0.1 increased the conversion rate from 16.1% to 76.0% for Knoevenagel condensation. The two reactions proceeded smoothly in the presence of deprotonated BSNC-700. The results also showed that the catalyst could be recycled for several times for Knoevenagel condensation. The results from this research will provide a guideline to develop bamboo shoot as a precursor to fabricate a superb solid base catalyst

Nitrogen Self-Doped Activated Carbons Derived from Bamboo Shoots as Adsorbent for Methylene Blue Adsorption

Bamboo shoots, a promising renewable biomass, mainly consist of carbohydrates and other nitrogen-related compounds, such as proteins, amino acids and nucleotides. In this work, nitrogen self-doped activated carbons derived from bamboo shoots were prepared via a simultaneous carbonization and activation process. The adsorption properties of the prepared samples were evaluated by removing methylene blue from waste water. The factors that affect the adsorption process were examined, including initial concentration, contact time and pH of methylene blue solution. The resulting that BSNC-800-4 performed better in methylene blue removal from waste water, due to its high specific surface area (2270.9 m2 g−1), proper pore size (2.19 nm) and relatively high nitrogen content (1.06%). Its equilibrium data were well fitted to Langmuir isotherm model with a maximum monolayer adsorption capacity of 458 mg g−1 and a removal efficiency of 91.7% at methylene blue concentration of 500 mg L−1. The pseudo-second-order kinetic model could be used to accurately estimate the carbon material’s (BSNC-800-4) adsorption process. The adsorption mechanism between methylene blue solution and BSNC-800-4 was controlled by film diffusion. This study provides an alternative way to develop nitrogen self-doped activated carbons to better meet the needs of the adsorption applications

Seroprevalence of Neutralizing Antibodies to Human Adenovirus Type 4 and 7 in Healthy Populations From Southern China

Human adenoviruses type 4 (HAdV4) and 7 (HAdV7) are two major respiratory pathogens and sporadically cause outbreaks of acute respiratory diseases. The neutralizing antibody (nAb) response to these two adenoviruses in civilian populations, which is important for dissecting previous circulations and predicting potential outbreaks, remains largely unknown. In this study, we generated replication-competent HAdV4 and HAdV7 reporter viruses expressing secreted-alkaline-phosphatase (SEAP), and established neutralization assays to investigate the seroprevalence of pre-existing nAb in healthy volunteers from Hunan Province, southern China. The seropositivity rates are 58.4 and 63.8% for anti-HAdV4 nAb and anti-HAdV7 nAb, respectively. High nAb titers (> 1000) were frequently detected in HAdV4-seropositive individuals, whereas most HAdV7-seropositive volunteers had moderate nAb titers (201–1000). The seropositivity rates of anti-HAdV4 nAb and anti-HAdV7 nAb increase with age, with individuals younger than 20 exhibiting the lowest seropositivity rates. Both seropositivity rates and nAb titers are comparable between different sex groups. Notably, HAdV4-seropositive individuals tend to be HAdV7-seropositive and vice versa. Because HAdV4 antisera showed no neutralizing activity to HAdV7 whereas HAdV7 antisera cannot neutralize HAdV4, a subgroup of individuals might be susceptible to infection by HAdV4 and HAdV7 and thus generate nAb to both of them. These results revealed the continuous circulation of HAdV4 and HAdV7 and the lack of protective immunity in more than 35% of people, which emphasized the surveillance of these two HAdVs and the development of prophylactic vaccines

Mechanical Properties of Natural Chitosan/Hydroxyapatite/Magnetite Nanocomposites for Tissue Engineering Applications

Chitosan (CS), hydroxyapatite (HA), and magnetite (Fe3O4) have been broadly employed for bone treatment applications. Having a hybrid biomaterial composed of the aforementioned constituents not only accumulates the useful characteristics of each component, but also provides outstanding composite properties. In the present research, mechanical properties of pure CS, CS/HA, CS/HA/magnetite, and CS/magnetite were evaluated by the measurements of bending strength, elastic modulus, compressive strength and hardness values. Moreover, the morphology of the bending fracture surfaces were characterized using a scanning electron microscope (SEM) and an image analyzer. Studies were also conducted to examine the biological response of the human Mesenchymal Stem Cells (hMSCs) on different composites. We conclude that, although all of these composites possess in-vitro biocompatibility, adding hydroxyapatite and magnetite to the chitosan matrix can noticeably enhance the mechanical properties of the pure chitosan

Chitosan Composites for Bone Tissue Engineering—An Overview

Bone contains considerable amounts of minerals and proteins. Hydroxyapatite [Ca10(PO4)6(OH)2] is one of the most stable forms of calcium phosphate and it occurs in bones as major component (60 to 65%), along with other materials including collagen, chondroitin sulfate, keratin sulfate and lipids. In recent years, significant progress has been made in organ transplantation, surgical reconstruction and the use of artificial protheses to treat the loss or failure of an organ or bone tissue. Chitosan has played a major role in bone tissue engineering over the last two decades, being a natural polymer obtained from chitin, which forms a major component of crustacean exoskeleton. In recent years, considerable attention has been given to chitosan composite materials and their applications in the field of bone tissue engineering due to its minimal foreign body reactions, an intrinsic antibacterial nature, biocompatibility, biodegradability, and the ability to be molded into various geometries and forms such as porous structures, suitable for cell ingrowth and osteoconduction. The composite of chitosan including hydroxyapatite is very popular because of the biodegradability and biocompatibility in nature. Recently, grafted chitosan natural polymer with carbon nanotubes has been incorporated to increase the mechanical strength of these composites. Chitosan composites are thus emerging as potential materials for artificial bone and bone regeneration in tissue engineering. Herein, the preparation, mechanical properties, chemical interactions and in vitro activity of chitosan composites for bone tissue engineering will be discussed

AI-based design of buck converter

Multi-objective optimization of buck converter was done in CCM working condition in many researches. However, few researches focused on the optimization in DCM. In this report, three-objective optimization designed based on the buck converter which worked in discontinuous conduction mode. The equations of PC, Pon, PCu, PFe were different from the equations in CCM or BCM. In the first steps of this project, I deduced those equations and prepared all the parameters which was useful in the part B, which was a part to generate Pareto front based on 3 dimensions, including power loss, cutoff frequency and volume. NSGA-II, a kind of AI technology, was applied to generate Pareto frontier in this project. NSGA-II is an elitist and fast GA (genetic algorithm) evolved from basic genetic algorithm. In this report, the process of using NSGA-II to generate Pareto frontier was showed in details, including how the crossover process worked and the analysis of crowding distance sorting. I chose three extreme cases as three models from all the points in Pareto front. Case 1 had the minimum of power loss, while cutoff frequency is minimum among all the solutions in case 2. And the volume of filter was the minimal figure in the last case. In the final section in my project, I did a simulated experiment by MATLAB to visualize the difference between the working results of three extreme cases. And this will provide help designers of buck converter to select the suitable pairs of L and C.Bachelor of Engineering (Electrical and Electronic Engineering

Multi-objective optimization for smaller, efficient and better performed design of buck-boost converters

Converters are essential components in DC-DC transformation and each objective of a converter plays an important role in the transformation. However, in most cases, improving one objective means sacrifices the others. As a result, the overall performance of the converters is not satisfied. The thesis proposes a method to optimized volume, efficiency, and cut-off frequency of LC-filter in buck-boost converter with full consideration of keeping three objectives on optimal conditions compared to the existed method. The Multi-objective optimization is for building a more portable, highly efficient, and better performance converter. For avoiding the interference of improving each objective and for obtaining optimal solutions with a fast process and better convergence, the author applies Non-dominated Sorting Genetic Algorithm-II to generate a Pareto frontier which could provide researchers a visualized figure to select the cases based on their demands. The multi-objective optimization results are compared with single-objective optimization results to verify the feasibility of the project.Master of Engineerin

Promoting Healthcare Workers’ Adoption Intention of Artificial-Intelligence-Assisted Diagnosis and Treatment: The Chain Mediation of Social Influence and Human–Computer Trust

Artificial intelligence (AI)-assisted diagnosis and treatment could expand the medical scenarios and augment work efficiency and accuracy. However, factors influencing healthcare workers’ adoption intention of AI-assisted diagnosis and treatment are not well-understood. This study conducted a cross-sectional study of 343 dental healthcare workers from tertiary hospitals and secondary hospitals in Anhui Province. The obtained data were analyzed using structural equation modeling. The results showed that performance expectancy and effort expectancy were both positively related to healthcare workers’ adoption intention of AI-assisted diagnosis and treatment. Social influence and human–computer trust, respectively, mediated the relationship between expectancy (performance expectancy and effort expectancy) and healthcare workers’ adoption intention of AI-assisted diagnosis and treatment. Furthermore, social influence and human–computer trust played a chain mediation role between expectancy and healthcare workers’ adoption intention of AI-assisted diagnosis and treatment. Our study provided novel insights into the path mechanism of healthcare workers’ adoption intention of AI-assisted diagnosis and treatment

Photoelectrical Properties of TiO2 Nanorods with an Array-cluster Double-layered Structure

Titanium oxysulfate (TiOSO4) was used as an inorganic titanium precursor to synthesize TiO2 nanorods on a transparent, conductive fluorine-doped tin oxide (FTO) substrate by a facile hydrothermal process. The TiO2 nanorod film was rutile phase and exhibited an array-cluster double-layered structure. Under the illumination of a solar simulator, the short-circuit photocurrent density of TiO2 nanorods maximized at 0.17 mA/cm2, which was over twice that of samples originating from organic titanium isopropoxide ［Ti(iPro)4］ under the same conditions. Multi-dimensional structure and the participation of inorganic oxysulfate (OSO4-4) anion contribute to the enhanced photocurrent response of TiO2 nanorod films